Numerous machines and processes exist for controlling the output of web product which is to be separated into bundles or "clips" of a desired product count. In certain industries such as the paper industry, the demand for a high volume of product (such as folded and stacked napkins, tissues, paper towels, and the like) has spurred the design and development of machinery which can produce stacks of web product at a much faster rate than was ever possible with earlier systems. Two examples of such systems are disclosed in U.S. Pat. No. 4,770,402 issued to Couturier and U.S. Pat. No. 5,730,695 issued to Hauschild et al., the teachings of which are incorporated herein by reference insofar as they relate to separation fingers and associated mechanisms. Both patents address design difficulties regarding machines which stack product into clips having a desired number of folded items per clip. Many systems (including those of Couturier and Hauschild) employ a pair of folding rolls located above a stacking platform and a number of fingers which are manipulated to stack a stream of web product being folded upon the platform. After a number of web items (such as interfolded napkins or tissues) are stacked upon the platform, a set of fingers is inserted into the stream and is positioned above the stack upon the platform to define a clip having a known item quantity. A new clip is then formed above the fingers as the completed clip is lowered and moved to downstream operations.
In the prior art systems employing the above-described elements and system arrangement, a design problem arises in connection with the function and operation of the separation fingers which separate a completed clip from a clip being stacked. With reference to FIG. 1, which illustrates a prior art separator system, it can be seen that conventional separator finger mechanisms typically rotate the separation finger 1 about a single axis 3 through a range of positions into and out of a product stream 5 passing from between two folding rolls 6, 7. It should be noted that only one separation finger 1 is shown in FIG. 1 for purposes of clarity. In fact, most conventional systems employ a number of separation fingers 1 aligned side-by-side in a series which extends into the plane of the page of FIG. 1. Also, although only one series of separation fingers 1 is shown on the left side of FIG. 1 (only one series is necessary to separate a completed clip from a new clip), an additional series of fingers can be located on the opposite side of FIG. 1 as a mirror image of the separation fingers 1. As disclosed in the Couturier patent mentioned above, multiple sets of separation fingers can be advantageously used for moving and parting the clips.
The path of motion taken by the separation fingers 1 is illustrated by the dotted line A shown on FIG. 1. Each separation finger 1 usually has a flat upper surface in order to permit a stack of product to be formed on top of the separation finger 1. The preferred flat upper surface and pivoting feature of the separation finger 1 results in the L-shape found in many conventional separation fingers 1.
For proper control of the product stream leaving the folding rolls 6, 7, it is necessary to have the separation finger surfaces (upon which the product is stacked) close to the nip 8 between the folding rolls 6, 7. This orientation ensures proper folding and stacking of the product after it leaves the folding rolls 6, 7. However, this design preference conflicts with the ability of the separation finger 1 to pivot about its axis 3. By placing the separation finger 1 close to the nip 8, the pivoting separation finger 1 interferes with the folding rolls 6. Prior art systems attempted to avoid this interference in various ways. For example, in the Couturier patent above, circumferential grooves are located in the folding rolls. The base of the circumferential grooves is indicated by way of example as dotted line B on FIG. 1. By locating the separation finger within a groove, the separation finger has adequate clearance in its pivoting motion so that it does not interfere with the folding rolls (see the relationship between dotted lines A and B FIG. 1). A design drawback to this solution is that the grooves effectively weaken the folding rolls. Especially where long folding rolls are called for in a system and/or where the folding rolls need to be operated at relatively high speeds, numerous grooves in the folding rolls increase the chance for roll sagging, imbalance, and even failure. Another design solution to the separation finger and folding roll interference problem is disclosed in the Hauschild patent mentioned above. In the Hauschild patent, two sets of separating and carrying forks are used one set on either side of the product stack being built. This design permits the forks to be made shorter and therefore less able to interfere with the folding rolls during fork movement. However, the Hauschild design requires two sets of separation fingers rather than one, and calls for a relatively complicated mechanism to properly position and insert the forks into the web stream (note how the forks must be positioned at a particular angle and position prior to being rotated into the web stream). Also, the short forks used in Hauschild are unable to fully support the stack being built thereon, as is evident from the gap between the forks when they are placed in their stackbuilding position.
The design examples discussed above serve to illustrate the conflicting requirements of separation finger apparatuses. Long separation fingers provide adequate support for stacked product and can result in a simpler system design, but create problems with finger and roll interference, and undesirable roll features such as weak rolls or rolls unable to operate safely at high speeds. Short separation fingers can help to avoid finger and roll interference, but typically require a more complicated and expensive design, can result in inferior stack support, and can create the need for more separation fingers.
In light of the above design requirements and limitations, a need exists for a separator finger apparatus and method which provides adequate support for stacked product, utilizes a minimum number of separation fingers, has a simple design in which roll strength and speed capabilities are not compromised, locates separation fingers close to the folding rolls in their stack-building positions, and ensures minimal interference between the separation fingers and the folding rolls during system operation. Each preferred embodiment of the present invention achieves one or more of these results.